Pathologic lesions caused by bovine viral diarrhea virus (BVDV) infections comprise a wide spectrum of type, degree, and, by implication, pathogenesis, including congenital defects, necrotic-erosive lesions in mucosal epithelia and skin, and reactive as well as degenerative changes in lymphoid tissues. At least some of the pathology may not be solely due to BVDV replication per se, but rather caused by a host response to the virus, particularly the production of pre-inflammatory cytokines.